A 94 GHz FMCW radar has been developed for an obstacle detection and warning system for civil helicopters. Validity of the radar is demonstrated by flight experiments. Power line RCS is measured at the distance farther than 500 m to determine specifications for a practical radar. Measured results have shown that the RCS becomes more than 15 dB larger than that for short range observation. It has also been shown that the RCS variation with incident angle by Bragg scattering still remains even for long distance observation.